If you read the linked post the complaint is that vendors like Apple and the developers of packages like PhantomJS regularly ship versions of WebKit that are months or years out of date. the jQuery dev team could fix every outstanding bug in WebKit and they would still have to ship compatibility hacks in jQuery for years-old builds of WebKit.
If you read the linked post the point is that if they fixed every outstanding bug via a JavaScript workaround, everybody else would have even less incentive to fix anything.
Also, if there is a long delay in the pipeline, that is no justification for even more delay in putting something into it, just like things being put into it quickly would be no justification for not trying to shorten that delay.
If you don't fix any bugs, but Apple etc. update overnight everything via WiFi or Ninjas, jQuery will still keep accumulating fixes for old bugs and explode - on the other hand, if you fix bugs quickly, even a 3 year delay with vendors means that jQuery will "only" have to carry fixes for bugs of the last 4-5 years, not for bugs that existed since the dawn of time.
I think that is not even the job of jQuery, anyway; it fixes bugs that have to do with using jQuery and plugins, providing a consistent baseline despite browser bugs.
